Yes, it is possible to contract an STI despite using a condom, especially if it was not used properly. Vaginal discharge, even if it is thick, may not necessarily be a sign of infection as it can vary depending on your hormonal cycle. It is important to note that many STIs can be asymptomatic, meaning they may not show any signs or symptoms. If you are concerned, there are clinics and health centers that offer free testing services. It is always a good idea to get tested regularly for STIs to ensure your sexual health.